A new paper led by undergraduate thesis student Benjamin Lehmann and graduate student Yao-Yuan Mao. We present a new method for abundance matching galaxies to dark matter halos, which includes a free parameter that can account for the concentration dependence of the galaxy-halo connection, and thus naturally can account for different levels of assembly bias. We show that this parameter can be constrained with clustering data, and that low redshift clustering measurements from SDSS prefer a moderate amount of concentration dependence --- more than would be indicated by matching galaxy luminosity to the peak halo mass, and less than would be indicated by matching to the peak halo circular velocity. We use new large high-resolution simulation boxes to show that statistical constraints on these models have been limited primarily by sample variance in the limited-size simulations, and not in the data.